Expat Focus provides information and resources for expatriates for a large number of countries, including Mexico. The website also hosts forums and blogs for expats.
InterNations — Your Expat Community in Mexico provides essential information with an option for paid registration with for the expat community. Membership allows you access to even more shared opportunities about living in the country.
Justlanded: Mexico offers resources and background on all aspects of moving, working, visas, and practical life in the country
Yucatan Living is an online lifestyle blog for English-language readers about living and working in the Yucatan, Mexico.
CheapestDestinationsBlog: Mexico is part of an excellent source by an expat, travel writer, and publisher livingin Mexico, Tim Leffel, and features many informative articles.
Numbeo: Mexico is a fine crowdsourced site that provides much aggregate and itemized information about the cost of living in the country, the main cities, and bigger towns which should help prepare you for the transition.
Visit Mexico is a slick Mexican tourism portal maintained by the Mexico Tourism Board.
Lonely Planet provides a lot of useful travel information on Mexico.
No Hay Bronca is a site hosted by Ted Campbell which offers informative posts about all aspects of traveling and living in Mexico. He also has written fine books on Cancun and the Yucatan.
Yucatan Today is a travel guide for Merida, Mexico and the Yucatan Peninsula where you'll find Spanish colonial cities and cathedrals, mayan ruins, haciendas, exotic birds, caves, and more...